1. Field of the Invention
The present invention relates to a laying device for laying line elements in a machine having a first member and a second member rotatable relative to each other about a rotation axis thereof, which is applied to the circumference of those members. The laying device according to the present invention is typically used for electric and/or fluid supply lines in a wrist portion of an industrial robot.
2. Description of the Related Art
For example, a wrist portion of an industrial robot (referred to simply as a “robot” hereinafter) includes a structure provided with a first member and a second member rotatable in relation to each other about a rotation axis. Several prior arts are known for laying one or more electric/fluid lines in the circumference of such members rotatable in relation to each other. Typical examples are shown in FIGS. 1-3.
In a first prior art shown in FIGS. 1A and 1B, an outer member A and an inner member B are coaxially disposed so as to be rotatable in relation to each other about a common rotation axis, and a cable (or line element) W is laid to be turned in a U-shape within a annular cylindrical gap formed between the members A and B. More specifically, a stationary securing part C is provided on one member (the outer member A in this case) while a moving securing part D is provided on the other member (the inner member B in this case). The cable W is supported by the stationary securing part C and the moving securing part D and has enough length to extend between them with an U-shaped folded portion thereof formed within the annular gap.
In some cases, a CableTrack rack or a conduit can be used together with the above construction. The U-shaped folded portion can be formed by turning the cable circumferentially in a plane perpendicular to the common rotation axis as shown in FIG. 1A or by turning the cable parallel to the cylindrical surface of the inner member B as shown in FIG. 1B. These types of prior arts are described, for example, in Japanese Patent No. 2647700 and Japanese Utility Model Registration No. 2597287.
In a second prior art shown in FIG. 2, an outer member A and an inner member B are coaxially disposed so as to be rotatable in relation to each other about a common axis, and a cable W is laid to extend longitudinally generally parallel to the common axis. Further, a stationary securing part C is provided on one member (the outer member A in this case) while a moving securing part D is provided on the other member (the inner member B in this case). The cable W is supported by the stationary securing part C and the moving securing part D. The cable W may be bent near either or both of the stationary securing part C and the moving securing part D in generally a 2-shape, an S-shape, or a Z-shape. This type of prior arts is described, for example, in Japanese Patent Publication Nos. 2001-353684 and 08-197482 and Japanese Utility Model Registration No. 2553843.
In a third prior art shown in FIG. 3, an outer member A and an inner member B are coaxially disposed so as to be rotatable in relation to each other about a common rotation axis, and a cable W is laid to extend in a coiled form about the common rotation axis. Further, a stationary securing part C is provided on one member (the outer member A in this case) while a moving securing part D is provided on the other member (the inner member B in this case). This type of prior arts is described, for example, in Japanese Patent Publication Nos. 05-116090 and 08-112796.
However, the above prior arts involve the following problems (1)-(3).
(1) In the case of using the technique in which the cable W is laid so as to be turned in a U-shape (the first prior art), a large space for laying the cable, as a whole, is required to form a U-shaped turned portion with a sufficiently small curvature. In the case of a small gap between the outer member A and the inner member B, if this configuration is applied to the cable W, the U-shaped turned portion thereof will have a large curvature, which can bring about a large load on the cable W thereby to cause a problem of shortening the life of the cable W.
(2) In the case of using the technique in which the cable W is laid so as to extend longitudinally and generally parallel to the common axis and its ends are fixed (the second prior art), unless the cable W has a length enough to absorb its torsion, the torsion will shorten the life of the cable W. For example, in a robot, an arm portion thereof has a certain size and is easy to ensure a space long enough to absorb torsion of the cable W, while a wrist portion or the like thereof is too short to ensure an enough long liner space.
(3) In the case of using the technique in which the cable W is laid so as to extend in a coiled form (the third prior art), a smaller number of turns of the coiled cable leads to greater change in the diameter of the coiled cable during the relative rotation between the outer member A and the inner member B. This can cause a problem that a large radial space is required. A larger number of turns of the coiled cable also involve a long cable. Further, in the case that the cable W contains many lines (cores) or a thick electric or fluid line, it encounters a problem that it is difficult to form the cable W into a coiled shape.